1. Field of the Invention
The present invention relates to heat exchange water and a heat exchange system for performing heat exchange with respect to an object of heat exchange such as machinery, air, or liquid.
2. Description of the Background Art
Heat exchangers for cooling objects of heat exchange such as machinery, air, or liquid are widely used in factories and laboratories in many fields. Conventionally, in these heat exchangers, water such as city water and industrial water are employed as the heat medium for performing heat exchange because water is safe to handle, inexpensive, and suitable as a heat medium due to its high specific heat and high heat transfer rate.
Conventional systems for supplying the heat medium, namely, the heat exchange water, are configured as shown for example in FIG. 11. Specifically, the heat exchange water is forwarded by a circulating pump 51 to a cooler 52 that cools the heat exchange water using water 521. The heat exchange water is cooled in this cooler. The heat exchange water is sometimes hereinafter referred to as the cooling water. Subsequently, the cooled heat exchange water (cooling water) is forwarded to a cooling device 57, and is used for cooling an object of heat exchange 571 passing through the cooling device 57. The heat exchange water after being used for cooling is transferred back to the inlet side of the circulating pump 51 through piping 54 connecting thereto and forming a circulation system. When the quality of the heat exchange water degrades within this circulation system, the water is partially or completely discharged through a discharge pipe 56. Make-up water is then supplied to the circulation system after being treated in the pre-treatment device 59.
Heat exchangers using conventional water as the heat medium have the following shortcomings.
(1) Water used as the heat exchange water contains dissolved oxygen or oxidizers such as hypochlorous acid and sodium hypochlorite dissolved therein for sterilization. By the oxidizing effects of these components, metal materials used in the water supply piping system and the liquid ends of the heat exchanger become oxidized. As a result, (i) oxide films or, when aggravated, tumorous protrusions are formed in the liquid ends. This greatly decreases the heat exchange efficiency, and increases resistance in the piping system (heat exchange system) to impede flow of a specified quantity of heat exchange water. In addition, (ii) the thickness of metal liquid ends is decreased by oxidation and dissolution. The mechanical strength of these components is thereby lost, possibly causing a fracture in the components which leads to leakage of the heat exchange water. Furthermore, (iii) problems in the heat exchange system such as filter clogging occur because of the generation of so-called xe2x80x9crusty waterxe2x80x9d and the increase in turbidity caused by metal fragments that have flaked off due to corrosion.
(2) To solve the above problems, facilities are often provided for adding chemicals such as rust-preventatives. These chemicals must therefore be constantly purchased and stocked, resulting in costs for both the purchase and the storage space. During blowdown of the heat exchange water bearing rust preventives, measures must be taken to minimize impacts on the environment caused by the discharge of such water.
(3) The concentration of dissolved oxygen can be reduced by deaerating the heat exchange water in order to prevent oxidation by dissolved oxygen. However, oxidation and corrosion of the metal materials cannot sufficiently be avoided by simply reducing oxygen dissolution.
(4) There are cases where algae and microorganisms proliferate in the heat exchange system, forming biological films on the liquid ends. This may cause decrease in the heat exchange efficiency and increase in resistance inside the pipes. Chemicals such as germicides must then be added, entailing increased costs and environmental problems as in the above (2).
(5) The flow rate of the heat exchange water circulating in the heat exchanger is usually set at a rate including margins such that the object of heat exchange can be cooled to below a predetermined temperature even when the object generates the maximum heat load. The flow rate is not separately controlled for discrete objects. Despite the fact that the heat radiation load amount of the objects varies widely depending on operating conditions, and that no heat is generated when the operation of the facility is stopped, it is typical in conventional systems that the heat exchange water is constantly circulated at a flow rate fixed according to the maximum heat radiation load. In other words, depending on the situation of operation, most of the heat exchange water may be circulating wastefully. Further, while the supplying temperature of the heat exchange water is usually room temperature, the exiting temperature is approximately 5xc2x0 C. higher than the supplying temperature. As it is necessary to minimize the difference between the supplying and the exiting temperatures of the heat exchange water, a high flow rate of heat exchange water is presently used in conventional systems. For these reasons, in factories having many installations requiring heat exchange, a heat exchange system for circulating heat exchange water at an extremely high flow rate must be provided. In order to circulate heat exchange water at a high flow rate, the circulation line for the heat exchange water must be made wide to reduce the fluid resistance of the piping, but with certain limits. To complement this, the compressing pressure of the compressing pump is typically increased. However, power consumption of the compressing pump increases in proportion to the pump discharge rate and the number of installed pumps. Accordingly, there exist problems such as high costs and large installation space required by large-capacity pumps and pipes having large diameters, and vibrations caused by large pumps. Moreover, the influence on the environment during blowdown of a large quantity of heat exchange water certainly cannot be neglected. As described above, heat exchange water and a supplying system for the water that are environmentally benign and can maintain a stable cooling effect at high efficiency for a long period of time were not conventionally available.
The purpose of the present invention is to provide heat exchange water that prevents oxidation and deterioration of metal materials used in pipes for supplying/circulating the heat exchange water or in the liquid ends of the heat exchanger. The heat exchange water should also suppresses growth of algae and microorganisms, and eliminate detrimental effects on the environment. Another purpose of the present invention is to provide a simple heat exchange system that can retrofit in existing systems and that minimizes cost increase. A further purpose of the present invention is to perform control for optimal temperature through adjustment of the flow rate of the heat exchange water to accomplish lower flow rate and lower pressure of the heat exchange water, so as to reduce installation space and vibration due to the pump and to achieve a heat exchange system that minimizes cost increase.
According to the present invention, in a heat exchanger for cooling an object of heat exchange such as machinery, air, or liquid, a reductive water having zero or negative standard oxidation-reduction potential determined by use of the hydrogen electrode standard, is used as the heat exchange water for performing heat exchange with the object of heat exchange.
According to the above, oxidation and deterioration of metal materials used in pipes for supplying/circulating the heat exchange water or in the liquid ends of the heat exchanger can be prevented. Growth of algae and microorganisms can be suppressed, and impacts on the environment can be reduced. Further, as the reductive water can be obtained by, for example, adding hydrogen gas to water, a simple heat exchange system is provided that can retrofit existing systems and that minimizes cost increase. It is to be noted that not only hydrogen gas but also but also other reducing agents may be employed.
In addition, by controlling the flow rate of the heat exchange water (cooling water) circulating in the heat exchanger (cooling device) for cooling the object of heat exchange, the temperature of the cooling water can be controlled at a desired temperature. In this way, the cooling water circulating in the cooling device can be best tailored for the intended purpose, allowing efficient heat exchange with the object of heat exchange. Such an arrangement contributes to cost reduction.